The present invention relates to a fuel cell assembly having at least one fuel cell with a cathode and an anode, and to a method for operating a fuel cell assembly.
Fuel cell assemblies having fuel cells count as the drive of the future on account of the fact that they emit substantially only pure water as waste product. For the proper and optimal operation of such a fuel cell assembly, the water balance and in particular the closed-loop control of the moisture within the fuel cell of the fuel cell assembly are important factors. For instance, in the event of inadequate moistening, the efficiency of such a fuel cell assembly can be reduced considerably, which can be associated with a poorer power yield and a high production of waste heat from the fuel cell assembly. In the worst case, in particular in the event of too low a moisture content, damage to the fuel cell of the fuel assembly cannot be ruled out either.
For this reason, it is necessary to monitor the moisture content of at least one fuel cell fluid and, if appropriate, to influence the same. Here, for example from DE 103 61 672 A1, it is known to use moisture sensors which monitor the moisture content of the fuel cell fluids, in this case hydrogen and air. The disadvantage with such moisture sensors is, however, that these moisture sensors are very inaccurate, in particular under saturated measuring conditions, i.e. with moisture contents of the fluid of about 100%. In the presence of liquid water in the fluid stream it is possible, for example, for droplets to occur, which are able to impair such a moisture sensor negatively over a not inconsiderable time period in such a way that said sensor is not able to supply any usable signal. In this regard, it is alternatively known from DE 10 2006 022 864 A1 to monitor the temperature variation of a coolant in a coolant flow path along a fuel cell and in this way to draw conclusions about a desired moisture content in the fuel cell and, if appropriate, to adjust the same. However, this assumes that the same temperature distribution prevails in the fuel cell as in the coolant. However, this cannot be ensured at every time during the operation of a fuel cell assembly, which means that this control method is susceptible to faults and is inaccurate.